PROJECT SUMMARY This career development award will allow the Candidate, Dr. Nathan Baertsch, to establish an independent research career focused on unravelling how the brain adapts to maintain breathing during disease. The training plan outlined in this award combined with the Candidate?s background in motor plasticity, respiratory physiology and rhythm generation make him ideally suited to successfully follow this career development path. The breathing rhythm is generated by periodic synchronization of excitatory interneurons in the preBtzinger Complex (preBtC). The search for the essential rhythmogenic mechanism has been a central question in the control of breathing field for over two decades. Although this search has revealed many important discoveries, it has overlooked perhaps one of the most fundamental characteristics of the network ? its ability to adapt. The amount of synchronization among preBtC neurons is not fixed, but depends on a dynamic interplay between excitatory and inhibitory connections, and the intrinsic membrane properties of preBtC neurons. How this life- sustaining neural network regulates this precise balance of synaptic and intrinsic properties to ensure breathing remains robust is not well understood. Based on preliminary data, we hypothesize that the distribution of the network generating inspiration is adaptable, and the balance between synaptic excitation, inhibition, and intrinsic bursting properties can be homeostatically tuned to compensate for chronic perturbations that threaten rhythmogenesis and breathing. This project will build on the candidate?s prior training in electrophysiology, pharmacology, and optogenetics by introducing state-of-the-art chemogenetic, imaging, and molecular techniques. Combining these strategies will allow the Candidate to use a multi-level approach to characterize changes in the distribution of inspiratory activity (Aim1) and identify changes in synaptic and intrinsic properties (Aim2) in the preBtC following chronic disruptions in neuronal activity. These in vitro experiments using a novel brainstem slice preparation will be complemented with in vivo experiments to explore how breathing adapts to chronic suppression of preBtC activity in the intact animal (Aim3). To help the Candidate achieve the research and career development goals of this proposal, he will receive strong mentorship from Dr. Nino Ramirez, a leader in respiratory rhythm generation with a successful mentoring track- record. The Candidate will also receive research and career development support from an advisory committee of established professors and former K-awardees that have transitioned to independence. These PIs all work closely with the Candidate and are experts in the chemogenetic, imaging, and molecular techniques that will be training components of this proposal. With full institutional support and the additional training, mentorship, and experience that this K-award will provide, the Candidate will be well positioned to successfully compete for R01-funding and establish an impactful independent research program.